By means of soles, shoes are provided with a lot of properties which, according to the specific type of the shoe, may be strongly varying in their effect. Primarily, shoe soles have a protective function. By their stiffness, which is higher than that of the shaft, they protect the foot of the respective wearer from injuries caused by sharp objects, for example, on which the wearer may tread. Furthermore, the shoe sole protects the shoe, as a rule, against excessive abrasion. In addition, shoe soles may improve the contact of a shoe with the respective ground and thus facilitate faster movements. A further function of a shoe sole may comprise providing certain stability. Moreover, a shoe sole may have a cushioning effect, so as to, e.g., absorb the forces emerging from the contact of the shoe with the ground. Finally, a shoe sole may protect the foot against dirt or spray water or provide a plurality of other functionalities.
In order to satisfy all these functionalities, different materials are known from the prior art which may be used for manufacturing shoe soles. Exemplarily, shoe soles made of ethylene-vinyl-acetate (EVA), thermoplastic polyurethane (TPU), rubber, polypropylene (PP) or polystyrene (PS) are mentioned here. Each of these materials provides a special combination of different properties which are more or less well suited for soles of specific shoe types, depending on the specific requirements of the respective shoe type. For example, the TPU is very abrasion-resistant and tear-proof. Furthermore, EVA is characterized by a high stability and a relatively good cushioning property. Furthermore, the use of expanded materials, in particular of expanded thermoplastic urethane (eTPU), was taken into consideration for the manufacture of a shoe sole. Expanded thermoplastic urethane is characterized by a low weight and particularly good elasticity and cushioning properties. In addition, according to WO 2005/066250, a sole of expanded thermoplastic urethane may be attached to a shoe shaft without needing any additional adhesives. Another example of a shoe sole on the basis of eTPU as well as a manufacturing method thereof are described in DE 10 2005 050 411 A1.
However, one disadvantage of the embodiments disclosed in WO 2005/066250 has to do with the fact that the properties of the sole are affected continuously in areas by the sole of expanded TPU and that a more detailed influence of the sole properties is not possible according to WO 2005/066250.
In order to further influence the properties of the sole selectively, the use of additional functional elements, such as, e.g., a reinforcing element, is known from prior art. Such a reinforcing element may, for instance, be glued on the bottom side of the sole so as to increase the stability of the sole in selected regions such as, e.g., the medial region of the midfoot. Such a reinforcement may serve to relieve the whole movement apparatus (e.g., foot, ankle, knee, tendons, ligaments and so forth), for example when jogging on uneven ground or in case of an over pronation of the foot.
For example, EP 1 197 159 B1 discloses a shoe construction method and shoe obtained thereof, among the various construction methods for these products by injection, whether open, semi open, or closed, incorporating a wedge, with or without a stiffening midsole for said wedge, attached to a stitching insole which is secured to the sole or intermediate outsole.
One disadvantage of the functional elements and sole configurations known from the prior art is, however, the fact that the shoe sole and the additional elements, which selectively influence the properties and the functionality of the sole, have to be manufactured separately and have subsequently to be bonded, e.g., glued together. This may restrict the possibilities of influencing the properties of the sole by the additional functional elements. This means, in particular, that the functional element cannot move independently from regions of the sole which are in contact with it. For example, this may lead to the effect that the additional element, though causing an improvement of the properties of the sole in a first direction, e.g. reinforcement in longitudinal direction, at the same time causes an undesired deterioration of the properties of the sole in a second direction, e.g. perpendicular to the first direction. This is true, in particular, for flatly designed elements. Furthermore, only such materials may be used which may be glued together. This restricts the selection of materials and hence the design possibilities of the sole and the shoe significantly. A further disadvantage of functional elements which are fixed or glued to the bottom side of the sole is that these elements may influence the behavior of the shoe negatively during contact with the ground. So, such an element may, for example, lead to a slipping of the foot on uneven ground (e.g. on stones or roots) and thus to a fall of the wearer.
Starting from prior art, it is therefore an objective of the present invention to provide better soles for shoes, in particular sports shoes. A further objective of the present invention comprises providing improved possibilities to influence the properties of shoe soles by means of additional elements.